(function(doc,win){
			var docEl = doc.documentElement,
			resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize' ,
			recalc = function(){
				var clientWidth = docEl.clientWidth;
				if(!clientWidth) return;
				if(clientWidth>640){
					clientWidth=640;
				}
				docEl.style.fontSize = 20 * (clientWidth / 320) + 'px';
			};
			if(!doc.addEventListener) return;
			win.addEventListener(resizeEvt,recalc,false);
			doc.addEventListener('DOMContentLoaded',recalc,false);	
})(document,window);